People can use minimum iLv DF setting to experience older fights at roughly the original difficulty. There isn't much value in experiencing older expansions as the were then because the game has always been the same in the ways that matter most. Old gear would regain its loot restrictions, weekly cap. Old versions of jobs is the biggest difference, especially ones that were reworked entirely. You could go back and mess around with those but it's not enough to necessitate its own server.